Method and apparatus to enhance spectral purity of a light source

ABSTRACT

A reflective filter serving as a multi-bandpass filter for a light source configured to emit light in a plurality of color primary wavelengths to improve color purity. The addition of a reflective/recirculation assembly reinforces and recirculates light not passed by the multi-bandpass filter back into a desired spectrum, which is subsequently passed by the multi-bandpass filter, or converts light not passed by the multi-bandpass into electrical energy for use by the system. The reflective filter, solely or along with the recirculation assembly, can be placed adjacent a conventional light source. Alternatively the multi-bandpass filter and the recirculation assembly can be placed in a modified light source, or placed in an optical stack along the path of light emission. Collimating structures that enforce the light into desired incident angle of attack onto the reflective filter can be included to enhance the efficiency of the reflective elements in the assembly.

RELATED APPLICATION(S)

This application is a divisional of the co-pending U.S. patentapplication Ser. No. 15/074,916, titled “Method and Apparatus to EnhanceSpectral Purity of a Light Source,” and filed Mar. 18, 2016, which ishereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to light sources, and morespecifically to enhancing the purity of the spectral components of alight source.

BACKGROUND OF THE INVENTION

Many lighting fixtures, portable lights and display panels use whitelight emitting diodes (LED's) as light sources. White LED's can beconstructed from junctions of various semiconductor material to producedifferent color spectral-peaks (wavelength bands of significantemissions) of light. The more efficient (on a watts/lumens basis) whiteLED's have followed the path invented by Shuji Nakamura, and pioneeredby Nichia Corp Japan. These white LED's were based on an Indium GalliumNitride (InGaN), AlGaInP and similar GaN junctions, characterized byconstituting a blue photon pump and a companion phosphor within the LEDassembly, or located remotely but within the light path of thephoton-pump. The emission of blue light (in the 430˜465 nm range) beingpartially absorbed by the phosphor particles (e.g. YAG phosphor,comprising of rare earth metal Yttrium, and Aluminium, Oxygen Y₃Al₅O₁₂)and re-emitted in a lower, broad wavelength range, centered aroundyellow 552 nm (e.g., exhibiting the Stokes shift, down-convertinghigher-energy blue light photons, into longer wavelength photons). Thecombination of blue and broad-yellow re-emissions generates what appearsto a typical human eye to be white light, by virtue of the use ofcomplementary blue and yellow colors (e.g., the broad spectrum shown atthe top right of FIG. 2).

One challenge of a Blue+YAG LED is that a blue-ish tint can be perceivedfrom these nominally “white” LED's. This tint is exacerbated over timeif the proportion of yellow produced by the YAG is reduced, or fades, orif the dominant spectral peaks shift with age. Another change causing aperceived shift away from white light can be blue emissions from thephoton pump fluctuating in wavelength or intensity, for example withsupply forward-voltage/current, temperature and/or duty-cycle inpulse-width modulation. By any means, producing an imbalance in theratio of the specific blue and yellow dominant spectral wavelengths oramplitudes alters the color ratio required to produce the desired shadeof white—termed the “white point.” Typically, the white-Point isexpressed as either CIE standard reference Illuminant D-point (forexample D65, or D50), or as a “color temperature” in degrees Kelvin (forexample D65=color temperature of 6504K).

Another challenge for forming high-performance white LED's is thereliance on rare-earth metals (e.g., Yttrium), which are geographicallysparse, creating a heavy dependence on a single region. Alternativephosphor arrangements based on a combination of red silicon nitrides (asper GE Corporations “KSF” phosphor) and green silicon alumina nitride(as per a and β-SiAION phosphor from Fujikara Corp.) have emerged in thespace, producing richer white through stronger, narrower red & greendominant primaries. The new phosphors come with additional challenges inthat the emission characteristics are uneven, and degrade more quicklyat independent aging rates. What is desirable is a solution that canproduce a selected color temperature of white light through selectiveprimaries, using existing or more readily available phosphor materials.

Organic LED's (OLED's), which are based on emissions of organicmaterials (instead of the Inorganic materials used in LED junctions),are rising in popularity as well due to improvements in intensity,luminosity per-mm² and per-Watt, and are competing with LED's as anotherviable light source. The challenges with OLED as a light source aresimilar to those of LED's, and further the organic electro-luminescentor electro-phosphorescent materials tend to aging more quickly (forexample dropping 10% in less than 1,000 hrs), accelerated through theaction of oxidization and humidity. Additionally, the materials used forthe primary colors have different efficiency and aging rates—blue inparticular aging as much as twice as fast as green, which degrades 10%faster than red—each affecting the color balance as the primariesdegrade differently. What is desirable is a solution that can produce amore stable selected color temperature of white light, through regulatedprimary emission.

Conventional lighting strategies for electronic liquid crystal displays(LCDs) provide for illumination for the display in one of threemodalities: direct backlight, front lit and edge lit. A direct backlightis configured with a light source (e.g. a LED, OLED orElectroluminescence (EL) layer) positioned directly behind a pane of thedisplay (typically a glass pane), such that illumination from the lightsource transmits through the pane. For a front lit system the lightsource is placed substantially in front of the viewing plane, typicallyin the front bezel along the inside-edge. Light from the front lightpasses into the display plane, through an optical stack, reflects offthe back-reflector and then passes out again through the pixels. An edgelit backlight positions the light source at one or more edges of adevice, and is designed to conserve both thickness, space, and powerconsumed by the device. A typical edge lit backlight has structure asdepicted in FIG. 1, which illustrates a schematic overview andcross-section of an edge-lit backlight and display. The display and edgelit backlight 20 are shown in cross-section A-A. A light source 22(e.g., an LED, OLED, CCFL, Laser or EL) is positioned along an edge ofthe display, and can be housed within a housing 24. The light source 22is positioned such that light emitted is directed toward an opticalstack 26 of the display, the optical stack 26 typically including anumber of layers. A light guide 28 is configured to direct illuminationfrom the light source 22 across the breadth of the display. The lightdirected from the light guide passes through layers of the optical stack26, which can include, for example, a diffuser layer 30, a brightnessenhancement layer 32 (e.g., brightness enhancement film (BEF)), a firstpolarization film 34, a liquid crystal film 36, and a secondpolarization film 38.

Typically, the light source 22 includes LEDs in a backlight bar (forexample, a string of LEDs along a PCB), arranged along an edge of thedisplay. The LEDs can be arranged along one, two, or all four edges ofthe display. As light from LEDs is directed into the light guide 28(which is often wedge-shaped), a series of microdivots along an exitingface of the light guide 28 causes light to scatter, directing some ofthe light to go forward through the polarization films 34 and 38, alongwith the liquid crystal film 36 (the combination of polarization films34 and 38, and the liquid crystal film 36 can be referred to as an “LCstack”). Often the light guide 28 includes a reflective surface (e.g.,ESR) to reflect light from back side of the light guide wedge toward theillumination side of the display. While edge- or direct backlighting maybe used for any LCD display, direct backlighting solutions do notrequire a light guide and tend to be more efficient at directing lightenergy through the optical stack to the viewer. However, directbacklight solutions are thicker and heavier and thus theseconfigurations are typically only used for TVs and computer monitorswhere display thickness is not as critical. Edge lit configurations areoften used for mobile devices, tablets, and laptops where weight andreduced thickness of the overall display is more important, and there isinsufficient room for a direct lighting solution.

A principle of operation for a liquid crystal display is to sample lightwith an aperture comprising two linear polarizers, and apolarization-controlling liquid crystal, in the optical stack. In oneLCD embodiment there is only one layer that relates to the colordeveloped in the display, that being the color filter. That is, what isdisplayed on the LCD in terms of color, and the range of colors (e.g.,the color gamut), is determined by the purity of the light source, andthe color filter that is present. In other LCD embodiments, for examplethose using color-field-sequential displays, there is no color filter,the LC layer still operates as an aperture, however the light source isselectively alternated to display each of the primary colors inrepeating order, in sync with the moment of displaying the pixels of theframe in that primary color. By either means the light source istherefore an important element in determining the color and quality ofthe image seen on an LCD display.

FIG. 2 depicts an exemplary formulation of red, green, and blue primarycolors for an LCD using a white light source in a conventionalbacklight. The light source shown is a white LED, which is the primarylight source in a modern display. In LCD display panels, thisbroad-spectrum white light is filtered in the display by color filtersat selected central wavelengths, typically corresponding to red, green,and blue wavelengths (e.g., 640, 532, and 467 nm). The incidentillumination from the light source dictates the characteristics of eachof the color filters, both in the amount of absorption of incidentillumination required, and in the breadth of the color filter (in termsof wavelengths passed). The illumination from the light source, filteredby the color filters, forms display primaries that are intended to beperceptually significant in intensity, so as to display the target colortemperature of white (an expression of the hue and shade of white, basedon the spectral emission characteristics at the given temperature of ablack-body emitter), when used in unison, but having broad spectrumscentered about the desired wavelengths.

Such light sources when used in conventional display backlights lead torelatively poor color saturation and intensity at the desired primarywavelengths of the display. The cause being the wavelength spread of theprimary colors being too broad, and not concentrated sufficiently at thedesired wavelengths spectrum to produce crisply defined tri-axial pointsfrom which can be rendered a gamut of colors. The conventional colorfilters included in the display break up the light source spectrum intoseparate colors on the display (e.g. in subpixel components of red,green, and blue) by absorbing light energy not of the desired spectralrange, typically expending the absorbed energy as heat. Conventionalefforts to improve the color of the display have increased the role ofthe color filter by increasing the thickness of the color filters asband-pass filters, or by use of filter material with stronger absorptioncharacteristics. While this can make the range of wavelengths centeredabout the desired wavelengths spectrum narrower (in terms of thepassband), because the color filter is an absorptive filter, a thickerfilter is needed to create a narrower bandpass, which reduces furtherstill the amount of light transmitted through the filter and ultimatelythrough the display. Additionally there is a physical limit to thethickness which a conventional color filter can be increased in an LCDcolor filter before it exceeds the space available in the coating areaof the optical assembly. For example, in order to achieve the DigitalCinema Initiative DCI-P3 standard for color gamut, the filter thicknessrequired in a conventional backlight can result in an additional 50˜75%reduction of transmitted light from light source, and thereby a 2×˜3.5×increase in backlight power can be required to produce an equivalentbrightness to a narrow gamut display. Moreover higher brightnessrequires more LED's, a wider bezel to contain more LED's, higher power,more cooling, and larger battery to maintain equivalent productoperating time for portable system—all of which contributing to highersystem cost, greater weight and reduced product user-friendliness. It isdesirable to solve the challenge of producing wider color gamut withhigher efficiency rather than simply increasing brightness and backlightpower.

In LED array display panels, the individual pixels are constructed fromgroups of LED's. For example each pixel includes one LED for each of theprimary colors of the sub-pixel. Such LED displays are typically used inwall displays or outdoor street advertising where brightness and sizeare required. In some embodiments each sub-pixel primary color LEDcontains a phosphor stimulated by a diode junction photon pump to emitin the desired primary color spectrum. In some configurations theprimary color is achieved through tuning the junction material, anddesign of the photon-pump, to emit directly in the desired spectralrange. The color spectrum output of such LED embodiments is variable dueto design and operating factors over the life of the LED, such as thevoltage applied at the diode junction. Alternatively, in LED's withphosphor elements, increased temperature of the phosphor causes aquenching effect that diminishes relative output and thereby the colorbalance between photon-pump and phosphor. The percentage duty cycle useof one primary color LED compared to other primaries alters the relativecolor output of each pixel group, causing a shift in white balance andcolor reproduction. The ability to tune operating spectral emissionranges of LED primaries to constrain at specific desired wavelengths,regardless of aging and usage characteristics, is highly desirable.

In OLED display panels of one configuration, the individual pixels arecreated from organic phosphor sub-pixels of each primary color (e.g.red, green, blue), where each sub-pixel color emission comes from anorganic phosphor stimulated by electric potential generated in thedisplay backplane. In OLED display panels of a secondary configuration,the pixel includes one or more organic phosphor elements producing whiteemission at each sub-pixel, which is then filtered by a color filterlayer arranged to pass wavelengths of the desired primary colors foreach sub-pixel—similar in function to the Color Filter in an LCD. Inboth configurations a key challenge for OLED arises as the individualsub-pixel elements age, in particular the sub-component organicphosphors age differently, for example blue phosphor tends to degradefaster than red or green. Additionally, the relative use of eachsub-pixel can disproportionally accelerate the shift in emissionspectrum according to the amount of relative usage. Hence colornon-uniformity and even “image sticking” are common problems whereby thecolor emission degradation over time becomes visibly noticeable to atypical human eye. The ability to tune operating spectral emissionranges of OLED primaries and constrain emission to specific desiredwavelengths, regardless of aging, and usage characteristics, is highlydesirable. In the secondary OLED configuration, the spectral output ofwhite sub-pixel OLED's is again limited by the absorptioncharacteristics in the absorptive color filter. The color gamut isdependent on the primaries thus filtered, and the energy absorbed by thecolor filter, which is effectively wasted, lost in heat. Current OLEDdisplays have reached limit of around 90˜100% of NTSC, and are notcurrently capable of rendering a wider color gamut, such as is neededfor DCI-P3 or BT.2020, which has been achieved with competing LCDtechnology using Quantum Dot particles. OLED displays have deeper blacksand better contrast ration than LCD's, and tend to have lower power inmobile applications. It would be advantageous to achieve an equally widecolor gamut for OLED displays.

SUMMARY OF THE INVENTION

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter.

Aspects of the present disclosure provide a method and device capable ofimproving transmitted color purity of light emission via a reflectivemulti-bandpass filter, for example enhancing the color purity of adisplay backlight light source and thereby the color gamut on a displaypanel, optionally while improving the brightness of the display panelvia intermediate recycling of unused reflected light wavelengths. Thesource can be used as a back-light shining through an imaging layer suchas in a Liquid Crystal Display panel, or as a front-light reflecting offan imaging layer such as in an eInk display. The light can be one of aplurality of lights used to cover segments or regions of a display. Thelight can be individual pixels as in an LED array display or an OLEDdisplay device. Additionally the light source can be a standalone lightsource, such as that found in a room, or in a streetlamp.

For convenience, aspects of the present disclosure are discussed in thecontext of lighting for a display. It will be appreciated by those ofskill in the art that the embodiments described are exemplary, and thatfurther embodiments are consistent with the spirit and scope of thepresent disclosure. For example, while the discussion herein regardinglighting of a display panel is directed toward an LED light source,embodiments according to the present disclosure are also able to bedirected toward display modalities including OLED, EL, cold-cathodefluorescent light (CCFL), cathode-ray phosphorescence (CRT),incandescent light, laser, or any other light source. Likewise, whilefor convenience the description herein is directed toward an edge-litbacklight display, embodiments of the present disclosure are readilyadapted to be compatible with direct backlight and front lit displays,as well as to applications in overhead lighting and projective light.

Further, the present disclosure is not limited to light sources fordisplays. At a basic level, embodiments according to the presentdisclosure are able to be adapted to preferentially configure the outputillumination of a general light source, by passing a selected single- ormulti-band of accepted wavelengths of the light source and by rejecting,via reflection, wavelengths outside the accepted band(s). Someembodiments include an energy recycling functionality, wherebywavelengths initially out-of-band are translated into in-bandwavelengths, which are passed by the selection filter. In this mannerconceivably any light source output can be modified, such as that ofindoor lighting or a street light. Consider for example a street lightwith a light source having a first native output spectrum. By filteringand/or recycling output illumination of the street light, one or both ofthe final output spectrum (e.g., apparent color spectrum) and energyefficiency of the street light can be enhanced. This can allow for alight source having an undesirable native spectrum but an efficient (orless expensive) operation, where an apparatus according to the presentdisclosure is able to modify the undesirable native spectrum to apreferred apparent color spectrum—e.g., to enhance the yellow-orangespectrum emission, relative to the blue spectral emissions, orconversely to shift-lower or decrease the spectral blue output range.This can be desirable for example in order to minimize disruption onnatural circadian rhythms on plants, animals, humans and otherorganisms, as caused by night lights with an unnaturally large bluecomponent.

An embodiment of the present disclosure includes a reflective filterserving as a multi-bandpass filter for light source illumination toimprove color primaries in a backlight for a display. The addition of areflective/recirculation assembly reinforces and recirculatesillumination not passed by the multi-bandpass filter back into theapparatus for conversion into a desired spectrum, which is subsequentlypassed by the multi-bandpass filter. The reflective filter, solely oralong with the recirculation assembly, can be placed adjacent aconventional light source. Alternatively the multi-bandpass filter andthe recirculation assembly can be placed internal to a modified lightsource, or placed in an optical stack of a backlight or frontlightassembly. Collimating structures that enforce the light into desiredangles of attack onto the reflective filter can be included, for exampleto enhance the efficiency of reflective filters constructed fromdichroic filter layers in an embodiment.

More specifically, an aspect of the present disclosure provides a lightrecycling assembly for enhancing spectral purity of transmitted light ofa display, including a first dichroic filter disposed in a light path ofa light source and operable to transmit light over a first passband ofwavelengths, and to reflect wavelengths not of the first passband. Thelight recycling assembly includes a conversion element including atleast one conversion particle, disposed to receive reflected light fromthe first dichroic filter, and operable to absorb light at a firstconversion wavelength and to emit light at a wavelength of the firstpassband.

In an embodiment the light recycling assembly includes a reflectingelement disposed to received emitted light of the conversion element andreflected wavelengths of the first dichroic filter, and operable todirect reflected light toward the first dichroic filter. In anembodiment the light recycling assembly includes a display color filter,the display color filter integrating the first dichroic filter. In anembodiment the light recycling assembly includes a photovoltaicconversion element including a particle operable to absorb light at aconversion wavelength band and to convert at least a portion of theconversion wavelength light into electrical energy. In an embodiment thelight source includes a photon pump operable to emit at photon pumpwavelengths, and the reflecting element includes a second dichroicfilter operable to transmit a second passband of wavelengths thatincludes photon pump wavelengths and to reflect wavelengths not of thesecond passband. In an embodiment the conversion element includes afirst particle adapted to absorb at least a portion of the photon pumpwavelengths and to emit light at conversion wavelengths other than thephoton pump wavelengths, and a second particle adapted to absorb lightof the conversion wavelengths and to emit light at a wavelength of thefirst passband. In an embodiment the first dichroic filter, theconversion element, and the second dichroic filter form an arrangementoperable to direct light in a light path, the light path including: afirst portion wherein light source light is incident upon the seconddichroic filter; a second portion wherein transmitted second passbandlight is incident upon the first dichroic filter; a third portionwherein the first passband light is transmitted by the first dichroicfilter toward the illumination side of a display panel; a fourth portionwherein reflected light from the first dichroic filter is incident uponthe conversion element; and a fifth portion wherein emitted light fromthe conversion element is incident upon the second dichroic filter. Inan embodiment the first dichroic filter, the conversion element, and thereflective element are substantially coplanar and form an arrangementadjacent to the light source. In an embodiment the first dichroicfilter, the conversion element, and the reflecting element are arrangedin an optical stack configuration including substantially coplanarlayers that are parallel to the illumination side of the display panel,and distal to a light guide with respect to the light source. In anembodiment the light source is disposed in a housing, and the housingincludes the reflecting element.

According to another aspect of the present disclosure, a method ofrecycling light for enhancing the spectral purity of transmitted lightof a display includes transmitting light over a first passband ofwavelengths by a first dichroic filter disposed in a light path of alight source; reflecting wavelengths not of the first passband, by thefirst dichroic filter; receiving reflected light from the first dichroicfilter by a conversion element including at least one conversionparticle; absorbing light at a first conversion wavelength; and emittinglight at a wavelength of the first passband.

In an embodiment the method further includes directing reflected lighttoward the first dichroic filter by a reflecting element disposed toreceived emitted light of the conversion element and reflectedwavelengths of the first dichroic filter. In an embodiment the firstdichroic filter forms a part of a display color filter. In an embodimentthe method further includes absorbing light at a photovoltaic conversionwavelength, and converting at least a portion of the photovoltaicconversion wavelength light into electrical energy, by a photovoltaicconversion element. In an embodiment the light source includes a photonpump emitting at photon pump wavelengths, and the reflecting elementincludes a second dichroic filter transmitting a second passband ofwavelengths that includes photon pump wavelengths and reflectingwavelengths not of the second passband. In an embodiment the conversionelement includes a first particle absorbing at least a portion of thephoton pump wavelengths and emitting light at conversion wavelengthsother than the photon pump wavelengths, and a second particle absorbinglight of the conversion wavelengths and emitting light at a wavelengthof the first passband. In an embodiment the first dichroic filter, theconversion element, and the second dichroic filter form an arrangementdirecting light in a light path, the light path including: a firstportion wherein light source light is incident upon the second dichroicfilter; a second portion wherein transmitted second passband light isincident upon the first dichroic filter; a third portion wherein thefirst passband light is transmitted by the first dichroic filter towardthe illumination side of a display panel; a fourth portion whereinreflected light from the first dichroic filter is incident upon theconversion element; and a fifth portion wherein emitted light from theconversion element is incident upon the second dichroic filter. In anembodiment the first dichroic filter, the conversion element, and thereflective element are substantially coplanar and form an arrangementadjacent to the light source. In an embodiment the first dichroicfilter, the conversion element, and the reflecting element are arrangedin an optical stack configuration including substantially coplanarlayers that are parallel to the illumination side of the display panel,and distal to a light guide with respect to the light source. In anembodiment the light source is disposed in a housing, and further thehousing includes the reflecting element.

According to another aspect of the present disclosure, an assembly forenhancing spectral purity of transmitted light of a display includes: alight source having an output surface operable to output light; a lightguide adapted to receive incident light from the light source at a firstsurface, and to emit light at a second surface; and a dichroic filterinterposed between the light source and an illumination surface of adisplay, the dichroic filter operable to pass a multi-band ofwavelengths of transmitted light, and to reflect wavelengths not of themulti-band.

In an embodiment the dichroic filter is disposed adjacent to the lightsource output surface and between the light source and the light guide.In an embodiment the dichroic filter is disposed within an optical stackbetween the light guide and the illumination surface of the display. Inan embodiment the assembly further includes a collimating structureinterposed between the white light source and the dichroic filter andadapted to collimate output light prior to incidence on the dichroicfilter. In an embodiment the assembly includes a photovoltaic conversionelement including a particle operable to absorb light at a conversionwavelength band and to convert at least a portion of the conversionwavelength light into electrical energy. In an embodiment the multi-bandof wavelengths corresponds with wavelengths in the visible spectrum. thedichroic filter consists essentially of a single fixed body.

According to another aspect of the present disclosure, a display systemincludes a display panel having an illumination surface and a lightemitting transmission surface; and a backlight, including: a lightsource operable to illuminate the illumination surface of the displaypanel; a first dichroic filter disposed adjacent the light source andoperable to transmit light source light over a passband of wavelengths,and to reflect wavelengths not of the passband; a second dichroic filteroperable to receive the transmitted passband light and to transmit atleast one selected wavelength of the passband, and to reflect otherwavelengths; and a recycling element including a particle disposed toreceive reflected illumination and operable to absorb at a firstwavelength and to emit at the at least one selected wavelength of thepassband. The first dichroic filter, the second dichroic filter, and therecycling element form an arrangement disposed between the light sourceand the illumination side of the display panel.

In an embodiment the recycling element includes a first particle adaptedto absorb light source wavelengths, and to emit recycled light at awavelength not of the passband wavelengths, and a second particleadapted to absorb recycled light and to emit light at a wavelength ofthe passband. In an embodiment the recycled light is of a shorterwavelength than the light source wavelengths. In an embodiment therecycled light is of a longer wavelength than the light sourcewavelengths. In an embodiment the light source wavelengths are visiblewavelengths and the first particle is adapted to emit light at invisiblewavelengths, and wherein the second particle is adapted to absorb lightof invisible wavelengths. In an embodiment the first particle and thesecond particle are disposed in adjacent deposition layers, and whereinthe first dichroic filter and the second dichroic filter aresubstantially coplanar having the adjacent deposition layers disposedtherebetween. In an embodiment the first dichroic filter, the seconddichroic filter, and the recycling element form an arrangement defininga light path for light source illumination, the light path including: afirst portion wherein light source illumination is incident upon thefirst dichroic filter; a second portion wherein transmitted passbandillumination is incident upon the second dichroic filter; a thirdportion wherein the at least one selected wavelength is transmitted bythe second dichroic filter toward the illumination side of the displaypanel; a fourth portion wherein reflected light from the second dichroicfilter is incident upon the recycling element; and a fifth portionwherein emitted light from the recycling element is incident upon thefirst dichroic filter. In an embodiment the passband includeswavelengths in the visible spectrum. In an embodiment the seconddichroic filter is operable to reflect IR wavelengths. In an embodimentthe system further including a light source conversion layer disposedbetween the first and the second dichroic filters, wherein the lightsource includes a photon pump and wherein the light source conversionlayer is operable to convert photon pump wavelengths into visiblewavelengths. In an embodiment a photovoltaic conversion elementincluding a particle operable to absorb light at a conversion wavelengthband and to convert at least a portion of the conversion wavelengthlight into electrical energy.

According to another aspect of the present disclosure, a display lightassembly includes a light source operable to illuminate an illuminationside of a display panel; a dichroic filter disposed in a light path ofthe light source and operable to transmit light over a first passband ofwavelengths, and to reflect wavelengths not of the first passband; arecycling element including at least one particle disposed to receivereflected light from the dichroic filter, and operable to absorb lightat a first wavelength and to emit light at a second wavelength; and areflecting element disposed to receive emitted light of the recyclingelement and reflected wavelengths of the dichroic filter, and to directreflected light toward the dichroic filter.

In an embodiment the assembly further includes a display color filter,the display color filter integrating the dichroic filter. In anembodiment the light source includes a photon pump, and the reflectingelement includes a first dichroic filter operable to transmit a firsttransmission passband of wavelengths that include photon pumpwavelengths, and to reflect wavelengths not of the first transmissionpassband, and wherein a second dichroic filter is operable to transmit asecond passband corresponding to the first passband of wavelengths, andto reflect light not of second passband. In an embodiment the recyclingelement includes a first conversion particle adapted to absorb reflectedlight from the first and second dichroic filters, and to emit light at athird wavelength, and a second conversion particle adapted to absorblight of the third wavelength, and to emit light in at least onewavelength of the first passband of wavelengths. In an embodiment thefirst dichroic filter, the recycling element, and the second dichroicfilter form an arrangement operable to direct light in a light pathincluding: a first portion wherein light source light is incident uponthe first dichroic filter; a second portion wherein transmitted secondpassband light is incident upon the second dichroic filter; a thirdportion wherein the first passband light is transmitted by the seconddichroic filter toward the light side of the display panel; a fourthportion wherein reflected light from the second dichroic filter isincident upon the recycling element; and a fifth portion wherein emittedlight from the recycling element is incident upon the first dichroicmirror. In an embodiment the assembly further includes a photovoltaicconversion element including a particle operable to absorb light at aconversion wavelength band and to convert at least a portion of theconversion wavelength light into electrical energy. In an embodiment theassembly further includes a color filter integrating the dichroicfilter.

According to another aspect of the present disclosure, an apparatus forenhancing spectral purity of transmitted light includes a housing; alight source disposed in the housing, having a fixed spectrum and anoutput surface operable to output light; and a dichroic filter disposedin the housing adjacent to the output surface, and operable to pass afirst multi-band of wavelengths of transmitted light, and to reflectwavelengths not of the first multi-band.

In an embodiment the first multi-band of wavelengths includes visiblewavelengths. In an embodiment the light source is adapted to emit lightover a broad emission spectrum. In an embodiment the passband width forpassbands of the first multi-band is selected according to apredetermined chrominance or hue ratio of the first multi-bandwavelengths. In an embodiment the passband amplitude for passbands ofthe first multi-band is selected according to a predetermined luminanceratio of the first multi-band wavelengths. In an embodiment apredetermined luminance ratio of the first multi-band wavelengths isgenerated according to wavelength-specific reflectivity constants of thedichroic filter for wavelengths not of the first multi-band. In anembodiment the housing includes an energy recycling element including atleast one conversion material disposed to receive reflected light fromthe dichroic filter, and operable to absorb and to convert light at afirst wavelength into electrical energy. In an embodiment the housingincludes a recycling element including at least one conversion materialdisposed to receive reflected light from the dichroic filter, andoperable to absorb light at a first wavelength and to emit recycledlight at a second wavelength. In an embodiment the housing includes areflecting element disposed to receive reflected wavelengths of thedichroic filter and the recycled light. In an embodiment the reflectingelement is disposed to direct light toward the recycling element. In anembodiment the reflecting element is disposed to direct light toward anoutput surface of the dichroic filter. In an embodiment the apparatusfurther includes a second dichroic filter placed after the recyclingelement wherein the second dichroic filter is adapted to permit thefirst multi-band of wavelengths, wherein the first multi-bandcorresponds with visible wavelengths. In an embodiment the conversionmaterial includes at least one particle exhibiting one of the Stokeseffect and the Anti-Stokes effect, the recycling element adapted toabsorb light not of the first multi-band of wavelengths, and to convertat least a portion of the absorbed light into a wavelength of the firstmulti-band of wavelengths. In an embodiment the conversion materialcomprises one of: phosphors; fluorophores; luminophores; chromaphores;and quantum dot particles. In an embodiment the dichroic filter isdeposited on an interior surface of the housing. In an embodiment thelight source comprises a plurality of point light sources arranged in apixel array of a display panel. In an embodiment the plurality of pointlight sources shares a common housing, and wherein the dichroic filteris disposed between the plurality of point light sources and thehousing. In an embodiment a second multi-band of wavelengths ispermitted to pass through the dichroic filter. In an embodiment thelight source is selected from one of an LED, an OLED, anelectroluminescent light, a cold-cathode fluorescent light, a laser, anincandescent light, and a fluorescent light. In an embodiment theapparatus further includes a photovoltaic conversion element including aparticle operable to absorb light at a conversion wavelength band and toconvert at least a portion of the conversion wavelength light intoelectrical energy.

In embodiments of the display backlight the light source includes anultraviolet (UV) photon pump, and the reflecting element includes afirst dichroic filter operable to transmit a first passband ofwavelengths that includes UV, and to reflect wavelengths not of thefirst passband. A second dichroic filter is operable to reflect UVwavelengths and permit transmission of a second passband that includesthe desired spectral wavelength bands. In an embodiment the lighttransmitted from the first dichroic element reaches at least one of:phosphor, luminophore, chromaphore, fluorophore, and quantum-dotparticles, which are configured to absorb UV wavelengths, and to emit inspectral ranges including wavelengths desired for emission in secondpassband through the second dichroic filter.

In embodiments the wavelengths correspond to emission peaks localized inat least one of the set of the red, yellow, green, cyan, blue and violetlight spectral ranges. However, it will be appreciated that there is nolimitation as to the wave-bands or wavelength of the emission peaks, norrestriction to a specific color. For example, while in one embodimentD65 white could be approximated using three primaries: 630 nm (red), 535nm (green) & 467 nm (blue); in another embodiment the same white-pointcould be approximated using 630 nm (red), and 495 nm (green-cyan).

In embodiments the backlight further includes a light source conversionlayer disposed between the first and the second dichroic filters,wherein the light source includes an ultraviolet (UV) photon pump andwherein the light source conversion layer is operable to convert UV intodesired relative emission strength in a desired component spectralranges. In an embodiment the desired spectral ranges include at leasttwo of a set of; red, yellow, green, cyan, blue, and violet, whichtogether form compound light of the desired spectral purity. In oneembodiment the spectral ranges include red, green, and blue, which inproportion, together form white light of the desired color temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present disclosure are illustrated by way of example,and not by way of limitation, in the figures of the accompanyingdrawings and in which like reference numerals refer to similar elements.

FIG. 1 is a schematic overview and cross-section of an edge-litbacklight and display according to the prior art.

FIG. 2 is a diagram depicting formulation of red, green, and blueprimary colors for a display from a white light source in a backlightaccording to the prior art.

FIG. 3 is a diagram depicting formulation of red, green, and blueprimary colors for a display from a white light source, reflectivefilter, and color filter in a backlight, according to an embodiment ofthe present disclosure.

FIG. 4 is a schematic diagram depicting an exemplary light sourceincluding an adjacent filtering apparatus for outputting narrow bandemission, according to an embodiment of the present disclosure

FIG. 5 is a schematic diagram depicting an exemplary light sourceincluding an arrangement (e.g., an adjacent film) for filtering andrecycling illumination from the light source, according to an embodimentof the present disclosure.

FIGS. 6A-6F are schematic diagrams depicting an exemplary light sourceincluding an adjacent arrangement (e.g., a standalone bar) for filteringand recycling illumination from the light source, the recyclingoccurring along a light path different from that of transmission forillumination, according to embodiments of the present disclosure.

FIGS. 7A-7F are schematic diagrams depicting an exemplary light sourceincluding a film having an adjacent reflective filter and one or morerecycling layers contained within a housing of the light sourceaccording to embodiments of the present disclosure.

FIG. 8 is a schematic diagram depicting an exemplary light source incross-section having a reflective filter as an added layer with existinglayers inside optical stack (e.g., adjacent to a polarizer of the LCpolarizer stack) according to an embodiment of the present disclosure.

FIG. 9 is a schematic diagram depicting an exemplary light sourceincluding an adjacent film for filtering and recycling illumination fromthe light source according to an embodiment of the present disclosure.

FIG. 10 is a diagram depicting a color gamut of a light source includingfive primary colors, along with the passbands of a multi-band reflectivefilter according to an embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the various embodiments of thepresent disclosure, examples of which are illustrated in theaccompanying drawings. While described in conjunction with theseembodiments, it will be understood that they are not intended to limitthe disclosure to these embodiments. On the contrary, the disclosure isintended to cover alternatives, modifications and equivalents, which canbe included within the spirit and scope of the disclosure as defined bythe appended claims. Furthermore, in the following detailed descriptionof the present disclosure, numerous specific details are set forth inorder to provide a thorough understanding of the present disclosure.However, it will be understood that the present disclosure can bepracticed without these specific details. In other instances, well-knownmethods, procedures, components, and circuits have not been described indetail so as not to unnecessarily obscure aspects of the presentdisclosure.

In the description the term particle refers to a material of anymaterial state including liquid, solid, plasma, and gas—whether insingular atomic or combined molecular form—and including but not limitedto any embodiment as solid particulate layer, film, coating, orsuspension. In an embodiment the recycling element contains particles ofat least one molecular compound, or quantum energy-level confinementconstruction, configured to absorb from one spectral wavelength band,and emit photons in a lower wavelength band exhibiting the Stokes shift.Alternatively, by action of the action of the Anti-Stokes effect, aparticle can absorb two or more photons, and emit one higher energyhigher wavelength photon. In an embodiment the recycling elementcontains at least one quantum dot particle, configured to absorb fromone spectral wavelength band, and emit in another spectral range, by aprocess typically including but not restricted-to action of the quantumexcitron-confinement effect. In an embodiment the recycling particlecontains at least one fluorophore compound configured to absorbelectromagnetic radiation from one spectral wavelength band, and emit inanother lower wavelength band, exhibiting the Stokes shift. In anembodiment the recycling particle is a luminophore containing at leastone luminescent molecule configured to absorb electromagnetic radiationfrom one spectral wavelength band, and emit in another lower wavelengthband, exhibiting the Stokes shift. In an embodiment the recyclingparticle is a chromaphore containing at least one molecule configured toabsorb electromagnetic radiation from one spectral wavelength band, andemit in another wavelength band.

As used in the present description, the term “multi-band” or“multi-bandpass” refers to a portion of the electromagnetic spectrumhaving energy concentrated around at least two central wavelengths. As anon-limiting example, bands of a multi-band can be centered about red(640 nm), green (532 nm), and blue wavelengths (467 nm), respectively.Greater or fewer bands are possible, as are other passband wavelengths.The width of the band can be as narrow as 2 nm, or as wide as 35 nmbased on the FWHM (Full-Width at Half-Maximum) measurement, for example.

Increased Backlight Primary Color Saturation

Referring now to FIG. 3, an overview diagram depicts formulation of red,green, and blue primary colors with the use of a reflectivemulti-bandpass filter, according to an embodiment of the presentdisclosure. At the top left graph I depicts a spectrum of a white lightsource. The white light source can be a white LED, which can be formedwith a blue light-emitting element and a fluorescent material used asthe white light source. Or, an RGB-LED formed with blue, green and redlight emitting elements can be used, or other white light sources knownto one of skill in the art can be used. Moreover other embodiments canuse a different set of three primary colors other than red, green, andblue (e.g. yellow, cyan, violet), and can use more than three primaries(e.g. at least three of a set of: red, yellow, green, cyan, blue andviolet).

Graph N depicts the transmission characteristics of a multi-bandpassfilter. According to embodiments of the present disclosure, themulti-bandpass filter is a reflective filter having high transmission(e.g., >75%, preferably >90% transmission) for passband wavelengths andstrongly reflecting non-passband wavelengths (e.g. >90% rejection). Themulti-bandpass filter can be, as a non-limiting example, a dichroicfilter (e.g., a dichroic mirror). A dichroic filter can be deposited ona glass substrate, where the dichroic filter has a thickness ofapproximately 10-20 microns, and wherein the glass is approximately 100microns in thickness. As depicted, the exemplary multi-bandpass filterincludes three passbands, centered about red (640 nm), green (532 nm),and blue wavelengths (467 nm), respectively. Greater or fewer passbandsare possible, as are other passband wavelengths. The width of thepassband can be as narrow as 2 nm, or as wide as 35 nm based on the FWHM(Full-Width at Half-Maximum) measurement, for example. Thecharacteristics of the filter bandpass being determined by designer as atrade-off for the cost, thickness of material deposition, number ofdeposition layers, and selection of the materials used for thedeposition layers.

The effect of the multi-bandpass filter on the light source emission isto transmit wavelengths centered at the passbands, while stronglyrejecting (reflecting) wavelengths not of the passbands. This results inthe narrow multi-band spectrum shown in graph II, which has peaks at thecenter of the passbands (e.g., at 640, 532, and 467 nm). This spectrumrepresents the light passed through the multi-bandpass filter and intothe backlight assembly. When modified by a set of color filters (shownin graph M), the narrow-band emission results in a spectrum as shown ingraph III. Graph III represents the primary colors (e.g., red, green,and blue) that are produced by a display with a backlight according toembodiments of the present disclosure, a display possessing anultra-wide color gamut.

The configuration and location of a multi-bandpass filter (e.g., adichroic filter) within a backlight can take one of severalalternatives. As is described further herein, a non-exhaustive listingof potential locations of the multi-bandpass filter includes: as anadditional film (e.g., adjacent to uniformity film) between light sourceand light guide; as a standalone bar between light source and lightguide; as an added layer with existing layers inside optical stack(e.g., adjacent to a polarizer of the LC polarizer stack); directlyunder or integrated with the color filter and before light passesthrough the filter, as one or more layers contained within a housing ofthe light source; and, directly on top of the surface of the lightsource within the housing (e.g. coating the junction material of anOLED).

According to embodiments of the present disclosure, a light source isable to include an arrangement (e.g., an adjacent film) for filteringillumination from the light source. Optionally, the adjacent film caninclude one or more components for recycling illumination of the lightsource, by which is meant translating illumination from outside apreferred spectral band or bands into the preferred band(s).

Referring now to FIG. 4, a schematic diagram depicts an exemplary lightsource 50 having an adjacent film (or bar) including a multi-bandpassfilter 56. The light source 50 can be an LED, for example a white LEDsuch as described above. The light source includes a photon pump, whichin FIG. 4 is shown as emitting at a blue wavelength. For brevity thedescription of FIG. 4 proceeds in terms of a blue wavelength photonpump, but it will be appreciated that photon pumps having other emissionwavelengths are possible, as are light sources that include photon pumpsof more than one emission wavelength (for example, two or more photonpumps, e.g., a blue die junction and a green die junction). A particle52 is contained within a housing of the light source 50, the particle 52for converting blue photons from the blue photon pump into otherwavelengths when excited, for example red and green wavelengths, whichtogether can convey the desired mix of red, green and blue primarycolors. There can be a combination of compounds present in particle 52,and the composition of the particles is designed to output selectedwavelengths from the input of the emitted wavelength of light source 50.In the case of multiple photon pumps (e.g., two or more die junctionseach emitting at a distinct wavelength) the combination of elements orcompounds present in particle 52 can be provided in order to convert thecombination of emitted wavelengths into a selected output. As anexample, for a light source having green and blue photon pumps and aselected output of red, green, blue, cyan, and yellow (RGBCY), particle52 is able to include elements or compounds that convert greenwavelengths and blue wavelengths into red, cyan, and yellow wavelengths,thereby generating the selected RBGCY output. Further, particle 52 isoptional, for example when a portion of the emitted wavelength of lightsource 50 is the preferred excitation wavelength.

According to embodiments of the present disclosure, the adjacent filmincludes a substrate 54 (e.g., a glass or plastic pane) positionedadjacent the LED, and the multi-bandpass filter 56 can be positionedadjacent the substrate 54. For example, the multi-bandpass filter 56 canbe a dichroic filter, which can be deposited on the substrate 54.According to some embodiments the adjacent film includes a filter 60,which is a bandpass filter selected to pass portions of the light sourcewavelength and to reject other wavelengths. For example, filter 60 is ablue-pass filter for a blue wavelength light source, rejectingwavelengths longer than blue (e.g., to selectively pass light around 467nm, with a width of 20 nm FWHM, require the filter to cutoff at467+10=477 nm), followed by another filter deposition layer adapted toreject wavelengths shorter than blue (to selectively pass light around467 nm, with a width of 20 nm FWHM, require the filter to cutoff at467-10=457 nm). An exemplary use of filter 60 is as an IR mirror,whereby IR illumination is retained within the light source housing andheat transmission beyond the light source 50 is reduced. In someembodiments the filtering apparatus is utilized within a backlight thatincludes a number of discrete light sources, each disposed within ahousing. In some embodiments a housing for the light source includes areflective layer 58 (e.g., ESR), which serves to reflect illuminationout of the housing.

In operation the light source 50 emits photons at a first wavelength(e.g., blue or ultra-violet), those photons being absorbed by theparticle composition 52 and re-emitted at one or more longer wavelengthsto form light emission peaks in the wavelength bands of the desiredprimary colors. The combined emission is incident on the multi-bandpassfilter 56, which passes selected bands of wavelengths, and reflectsout-of-band wavelengths. As shown in FIG. 4, the multi-bandpass filter56 passes narrow band emissions centered on 467, 532, and 630 nm,corresponding to three primary colors (e.g., RGB) with a bandwidth lessthan 20 nm FWHM for each emission peak. In this manner more saturated,intense primary colors are propagated, for example to a backlight device(e.g., to the remainder of the backlight optical stack), and onto theillumination side of a display panel.

Recycled Illumination Via Up- and Down Conversion of Out-of-BandWavelengths

The use of a highly reflective multi-bandpass filter, in contrast to anabsorptive filter, means that energy of the light source illuminationwavelengths not of the passbands (e.g., those not centered around red,green, and blue, for example) is not lost, but rather reflected backtoward the light source. An opportunity therefore exists to capture someof this energy and to transform it into useful light, for example, toconvert light source illumination outside of the passbands into one ormore of the wavelengths transmitted by the multi-bandpass filter. Such aprocess is termed herein “recycling” or “recycled illumination,” and canbe effected via employing the Stokes shift, the anti-Stokes shift, and acombination of these, as described below. As is known in the art, theStokes shift is a process wherein a material absorbs a photon of a firstwavelength, some of the excitation energy is expended increasing thevibration of the particle molecules, and then at the lower quantumenergy states the material re-emits a photon of a second wavelength,where the second wavelength is lower energy than the initial excitationenergy and this greater than the first wavelength (that is, the emittedphoton has undergone a red-shift to a longer wavelength). In contrast,the anti-Stokes shift is exhibited wherein a material absorbs twophotons at a first wavelength, and emits one photon at a secondwavelength that is less than the first wavelength (e.g., the emittedphoton is more energetic than absorbed photon, on a per-photon basis).

One manner of performing this change is via the use of a phosphor orphosphors that exhibit the Stokes and/or anti-Stokes effect. Other meansof changing, refining, eliminating, concentrating or tailoring thespectral band are also consistent with the spirit and scope of thepresent disclosure, and particle 52 can be one or more particles orcompounds, including: compounds that exhibit effects such as quantumwell excitron confinement (as used in Quantum Dots); phosphorsexhibiting phosphorescence under excitation (and in some cases willcontinue to emit for milliseconds to hours after excitation has ceased);luminophores exhibiting luminescence, in particular photo-luminescentmaterials that absorb photons and re-emit at another wavelength whileunder excitation; fluorophores exhibiting fluorescence emission underexcitation, usually from an electronic relaxation from a higher energywavelength (typically shorter in duration than phosphorescence, lastingin the order of nanoseconds); and chromaphores, which absorb certainwavelengths while transmitting or reflecting other wavelengths.Materials that exhibit these characteristics are known to those of skillin the art, and the particular wavelengths absorbed and emitted can beselected based on selection of the material (or combinations ofmaterials) used in the application herein referred to as particles.

According to embodiments of the present disclosure, materials thatexhibit the Stokes effect, as well as or in addition to those thatexhibit the anti-Stokes effect, can be used in combination with thereflected out-of-band wavelengths of the light source in order torecycle the illumination and capture more usable energy from the lightsource. In overview, a backlight operating in this manner includes alight source having illumination that is filtered by a reflectivefilter, and one or more materials that receive the reflected (that is,out-of-band) illumination and convert some of the reflected illuminationinto one or more wavelengths that are subsequently transmitted by thereflective filter—that is, converting out-of-band illumination intopassband illumination. For example a phosphor that absorbs in a broadblue wavelength band and emits in green wavelength, can be adapted torecycle, absorb, and to be excited by reflected light not of the firstdesired narrow blue wavelength band, and to re-emit this energy aroundthe desired green wavelength band. Similarly a particle adapted toabsorb reflected light not used from the broad green wavelength band,and re-emit around a desired red wavelength, can be used to recyclereflected light not of the first blue narrow band, and not of the secondgreen narrow band, and re-use such energy in the desired narrow redwavelength. It will be appreciated to those skilled in the art that thismethod is not restricted to just three primary narrow wavelength bands,but can recycle light for use by a plurality of primary bands, using aplurality of particles tailored for excitation by reflected light in anyof the unused ranges, and re-emit in other desired wavelengths.

Additionally, in embodiments a particle that is excited by visiblelight, and has an emission range in the infrared and near-infraredspectrum can be adapted for excitation by any of un-recycled visiblelight, and emission into the infrared spectrum. For example a phosphorparticle adapted for excitation by near-infrared and infrared, such asY₂O₂S: Yb, Tm (excitation in 900˜980 nm, emission in 460˜480 blue), andphosphor such as YF₃: Er, Yb (excitation in 900˜1000 nm, emission in540˜560 green), and phosphor such as YbOCl: Er (excitation in 900˜980,emission in 640˜680 red), will re-emit in desired visible wavelengthsthrough Anti-Stokes effect.

Alternatively in other embodiments a luminophore that is excited bylonger wavelengths (e.g. red to near infrared) visible light, and has anemission range in desired visible wavelengths through Anti-Stokeseffect, can be adapted for excitation by any of un-recycled visiblelight, and emission into the desired visible wavelengths throughAnti-Stokes effect.

According to an embodiment, recycling can include conversion of photonenergy into electrical energy by a converting material (e.g., via aphotovoltaic element). The converting material is able to be configuredto absorb emission wavelengths not of the passbands (e.g., outside of atransmission multi-band)—for example, the converting material can absorbUV and/or IR wavelengths, and convert a least a portion of the absorbedwavelengths into electrical energy. It will be appreciated that thiselectrical energy harvesting can be accomplished using appropriatematerials, and that particle 52 as described herein can include thisfunctionality.

Referring now to FIG. 5, an embodiment according to the presentdisclosure includes a light source 50 including an arrangement (e.g., anadjacent film) for filtering and recycling illumination from the lightsource a recycled illumination. Adjacent light source 50 are twosubstrate layers 54 and a particle 52. A reflective filter 56 ispositioned at a distal side (with respect to the light source) of theoutermost substrate 54. The reflective filter 56 can be, for example, amulti-bandpass filter of dichroic construction. The inner sides of thesubstrates 54 are coated with one or more materials that modify thewavelength of absorbed light (e.g., materials that exhibit the Stokesshift, the anti-Stokes shift, or a combination of these) to convertlight from one wavelength into another. The inner side can also becoated with converting Chromaphore material to absorb photons of onewavelength and convert into re-emission in another wavelength. The innerside can also be coated with a photon absorbing material to convertlight into electrical energy. As shown, the inner substrate 54 is coatedwith a first downconverting material 62 (e.g., a first particlecomposition), and the outer substrate 54 is coated with a secondupconverting material 64 (e.g., a second particle composition).Materials 62 and 64 are able to be composed of similar materials asthose described herein regarding particle 52. The light source 50 can bepositioned in a housing, which can be coated with reflected coating 58.As shown, particle 52 is present as a coating on substrate 54, that is,remote from the light source 50. Alternatively, particle 52 can bepresent within the light source 50 housing, as is known in the art andshown and described regarding FIG. 4.

In operation, illumination emitted from the light source is transmittedthrough the substrates 54 and conversion materials 62 and 64, and isincident upon reflective filter 56. Reflective filter 56 passeswavelengths of the one or more passbands, and reflects otherwavelengths. The passed wavelengths of filter 56 can be used as theprimary colors of a display, for example (e.g., edge-lit, backlit, orfront-lit display), or as the final apparent color of an illuminationsource (e.g., an office lamp or a street lamp). The reflectedwavelengths are directed back toward the substrates 54 and conversionmaterials 62 and 64. If conversion materials are selected for the Stokeseffect, some of the reflected illumination will be absorbed andre-emitted at a longer wavelength (e.g., UV absorbed and emitted in thevisible spectrum). If conversion materials are selected for theanti-Stokes effect, some of the reflected illumination will be absorbedand re-emitted at a shorter wavelength (e.g., IR absorbed and re-emittedin the visible spectrum). The particular conversion materials used canbe selected based upon the light source spectrum, the passbands of thereflective filter 56, and the desired recycled illuminationcharacteristics.

The configuration shown in FIG. 5 can include a reflective filter 60.The reflective filter 60 can be immediately adjacent the light source,and can serve as a first filter for light source illumination, as wellas a mirror for selected wavelengths of reflected illumination fromreflective filter 56. Reflective filter 60 can be a passband filter, forexample passing all wavelengths shorter than UV (e.g., rejecting longerthan UV wavelengths). In this manner all wavelengths shorter than UV arepropagated to the reflective filter 56, and any re-emitted wavelengthsof greater wavelength (emitted from conversion material 62 and/or 64)will be reflected within the space between reflective filter 56 andreflective filter 60. In this manner a recirculation chamber is formed,defined by the space between the reflective filters 56 and 60 andincluding conversion materials 62 and 64. Rejecting longer-than UVwavelengths leads to limiting or removing IR wavelengths from the lightsource and can reduce the amount of heat buildup in the display, whileat the same time making the other wavelengths available for reflectionby the reflective filter 56. In another embodiment, light source 50 isof a blue wavelength and filter 60 acts as a notch passband, rejectingvisible and invisible light other than blue including both UV and IRwavelengths. The described passband and rejection wavelengths are merelyexemplary, and any particular passband and rejection wavelengths can beselected based on the desired wavelengths ultimately to be transmittedto illuminate a display.

According to embodiments of the present disclosure, conversion material62 operates to convert reflected illumination into IR wavelengths, whichin turn are reflected by both reflective filters 56 and 60. Conversionmaterial 64 operates to convert IR wavelengths into one or more of thepassband wavelengths, which are transmitted through the reflectivefilter 56. In an embodiment, the re-emission wavelength of conversionmaterial 64 corresponds with the least intense primary natively producedby the light source (e.g., the red portion of the spectrum as shown inFIG. 3). In this manner portions of the light source spectrum havinglower intensity can be bolstered by the recycled illumination, therebydeveloping a spectrum of more uniform intensity. A greater number ofconversion materials can be present, each of which can serve to convertIR wavelengths into a selected passband wavelength (e.g., one of red,green, and blue).

Alternatively, the direction of wavelength conversion can beopposite—that is, a conversion material can convert reflectedillumination into UV wavelengths, which can be reflected by reflectivefilters 56 and 60, and another conversion material can convert UVwavelengths into one or more of the passband wavelengths. An advantageof down-coversion is a higher efficiency of the Stokes shift, ascompared with the anti-Stokes shift which is minimally half theefficiency of the former, requiring two photons to produce one, but incontemporary phosphors is typically on the order of sub-10% efficiency.

While FIGS. 4 and 5 illustrate both elements 62 and 64 for downcovertingand upconverting emission wavelengths from light source 50, it should beappreciated that in some embodiments only one conversion direction isenabled, by the presence of downcoverstion particles 62 only (oralternatively, upconversion particles 64 only). Multiple convertedwavelengths can be produced from the light source 50 with the use ofmultiple converting layers of the same type, e.g., downconverting layers62. According to embodiments of the present disclosure, conversion oflight source 50 emission wavelength(s) to wavelengths of the one or morepassbands is effected by cascading conversion particles—that is, aseries of particles 52, each absorbing and emitting at distinctwavelengths, can work in conjunction with the light source 50 and thereflective filter 56 to convert light source 50 wavelength(s) into theselected wavelengths of the passbands. This is possible without use ofthe anti-Stokes effect, by simply recycling light source 50 illuminationthrough a cascaded series of particles, organized with overlappingexcitation and emission ranges (or other combinations of conversion,absorption, or reflection materials).

For example, an embodiment similar to those depicted in FIGS. 4 and5—but without the upconverter element 64—can include light source 50 asa 360˜400 nm near-UV Photon Pump, with illumination incident upon afirst filter 60 (e.g., a dichroic UV band-pass, where all otherwavelengths are reflected). A first conversion material 62 (e.g., afirst downconverting phosphor) is excited by UV wavelengths, and emitsblue wavelengths. This blue light is incident upon the multi-bandpassfilter 56 (e.g., a dichroic filter), for example corresponding topassbands of blue 467 nm, green 532 nm, red 630 nm, having+/−20 nm FWHMnarrow bandpass. Reflected blue light not of 467+/−20 nm is incidentupon a second conversion material 62 (e.g., a second downconvertingphosphor) that is excited by UV/blue wavelengths, and has greenemission. This emitted green light is incident upon the multi-bandpassfilter 56, and reflected green light not of 532+/−20 nm (as well as theblue light not of 467+/−20 nm) is incident upon a third conversionmaterial 62 (e.g., a third downconverting phosphor) that is excited byUV/blue/green wavelengths, and has red emission). The red illuminationis incident on the multi-bandpass filter 56.

The red illumination can be further modified according to the following.Reflected red light not of 630+/−20 nm can be incident upon a fourthconversion material 62 (e.g., a fourth downconverting phosphor) that isexcited by red/green wavelengths, and emits in the IR. The IR emissionis then incident upon the multi-bandpass filter 56. In some embodiments,the multi-bandpass filter 56 is tailored to pass the emitted unrecycledwaste light out, for example as invisible infrared, and in a range thatproduces little heat, such that this light is not recycled by theassembly.

Alternatively, the reflected red light not of 630+/−20 nm can beincident upon a fourth conversion material (e.g., a fourth phosphor)that is excited by red/green wavelengths, and emits in the IR, and theassembly further includes an optional photovoltaic element (e.g., 57)adapted to absorb IR radiation and to generate electrical power.

While the above describes a UV light source 50 embodiment, a similarapproach can be implemented using a blue light source 50 (or indeedother light source 50 wavelengths). The conversion material(s) 52, thefirst filter 60 and the multi-bandpass filter 56 can be tailored torecycle illumination outside of the passbands. One reason that a bluelight source can be preferable is that blue light sources produce morephoton's per watt than do UV light sources. Additionally, contemporaryphosphors for conversion from blue wavelengths are better understood. UVlight sources can be preferable to Blue light sources in view of thefact that contemporary blue light sources tend to have a wider emissionbandwidth, and also blue light source performance can vary based on tempand voltage. An embodiment of a backlight according to the presentdisclosure includes an arrangement of reflective filters and recyclingelements that avoids degrading input light of the light source.Degradation can occur because the recycling element (e.g., phosphors)not only recycle reflected light, but can also absorb some of thedesired light that is incident by the light source. Therefore, aconfiguration of the present disclosure includes placing the recyclingelement out of the transmission light path, generating a recirculatinglight path circuit.

Referring now to FIG. 6A, a recycling element is placed adjacent a lightsource 50. The light source optionally includes a reflective surface 58(not shown). A first reflective filter 56, a second reflective filter60, remote conversion particles 52 and conversion materials (e.g.,phosphors) 62 and 64 are all disposed on substrates 54 (e.g., glasssubstrates), which are arranged in a triangular shape. The triangulararrangement forms light paths such that up- and down-conversion ofillumination does not occur along a transmission light path (e.g., lightpath to a display). While the arrangement shown is triangular, otherarrangements that place the up- and down-conversion of reflectedillumination out of the transmission path are also possible. One or moreof the substrates 54 can include a reflecting material 58.

In operation, as shown in FIG. 6B, illumination from the light source 50is incident upon the second reflective filter 60, which passeswavelengths within a passband and reflects other wavelengths. As shownin FIGS. 6C and 6D, the transmitted wavelengths are incident upon theremote particles 52, which convert incident illumination to the desiredprimary wavelengths (e.g. at least three of a set of red, yellow, green,cyan, blue and violet wavelengths). The primaries propagate to the firstreflective filter 56, which passes wavelengths of the passband ofreflective filter 56 (e.g., a multi-band corresponding to narrowbandprimary wavelengths), and reflects other wavelengths. As shown in FIGS.6E and 6F, reflected wavelengths from the reflective filter 56 aredirected toward a recycling element including conversion materials 62and 64, which function to up- and down-convert some of the reflectedillumination into the passband of the reflective filter 56. Thisrecycled illumination is then reflected from reflective filter 60, andthe wavelengths within the passband of reflective filter 56 aretransmitted on through the backlight. In general, the proportion ofparticles within the recycling element (e.g., proportion of conversionmaterials 62 and 64) is tailored along with the light source emissionspectrum, such that the finally transmitted wavelengths have the desiredproportions of primaries.

Recycled illumination conversion materials 62 and 64 are also able to belocated within the housing of a light source (e.g., within a modifiedLED housing). FIGS. 7A-7F depict a light source having recyclingelements within a light source housing, according to embodiments of thepresent disclosure. Referring now to FIG. 7A, a light source 50 islocated in a housing that includes particle 52 for converting lightsource 50 emission into broad spectrum emissions (e.g., from bluewavelengths into red and green). The housing further includes down- andup-conversion materials 62 and 64 (e.g., phosphors exhibiting Stokes andanti-Stokes effects). Reflective multi-band filter 56 (and optionally,bandpass filter 60) is located adjacent the light source, for example ona substrate film or bar 54. In operation, as shown in FIG. 7B, particle52 absorbs light source 50 emission and generates at least one spectrumemission from absorbed radiation. As shown in FIG. 7C, the emissions arepropagated to the multi-bandpass filter 56, which transmits narrowprimary passbands (e.g., 467, 532, and 630 nm) while reflectingout-of-band wavelengths within the housing. As shown the apparatusincludes bandpass filter 60, which serves to pass wavelengths shorterthan IR (e.g., functions as an IR mirror), however the presence offilter 60 is optional. FIG. 7D depicts the absorption and excitation byvisible wavelengths of the down-conversion material 62, which re-emitsradiation in the IR spectrum. The re-emitted IR propagates throughoutthe housing of the light source 50, with reflective surface 58 andfilter 60 aiding in containing the IR radiation within the housing. FIG.7E depicts the absorption and excitation by IR wavelengths of theup-conversion material 64, which re-emits radiation in the visiblespectrum (e.g., 467 nm). As shown in FIG. 7F, the re-emitted visiblewavelengths propagate throughout the housing of the light source 50,causing absorption and broadband re-emission by particle 52. Thisbroadband emission is filtered by multi-bandpass filter 56 to generatenarrow band emissions, and the cycle continues to repeat.

As has been described in several aforementioned embodiments, bothreflective filters and recycling elements can be located at variouspositions within an illumination system, for example a backlight of adisplay. Referring now to FIG. 8, an embodiment including multi-bandpassfiltering and recycling layers positioned within the optical stack of abacklight is depicted. As shown, a light source 50 is adjacent a lightguide, having a uniformity film placed therebetween. Adjacent the lightguide toward a reflector (e.g., ESR reflector) is a film layercontaining down- and up-conversion materials 62 and 64. These materialscan be, for example, deposited on a glass or plastic pane of the opticalstack. In a direction toward the LC stack of the backlight is a layercontaining the multi-bandpass filter 56 (e.g., narrow emission bandpassof red, green, and blue wavelengths). In operation, broadband lightemitted from light source 50 propagates through the uniformity film andinto the light guide, from which it is substantially evenly distributedacross the surface of the optical stack. The broadband illuminationincident upon filter 56 is filtered such that the narrow band emissionsare passed, while other wavelengths are reflected backward. Thesereflected wavelengths, upon incidence at conversion materials 62 and 64,are up- and down-converted to be re-emitted in desired primary coloremission wavelength bands, as has been described herein. Thesere-emitted primary emissions are reflected back toward the second filter56, which passes the accepted narrow band primary emissions and reflectsout-of-band wavelengths, and the cycle repeats. In this manner both thenarrow band filter, and the recycling of unused wavelengths from thelight source 50, occur with the optical stack of the system (e.g., thebacklight of a display).

In an embodiment a photovoltaic layer (not shown) is introduced into therecycling element, such that unused light energy reflected from theprimary emissions bandpass filter can be converted to electrical energy,which can be otherwise reused within the system. The reflectedwavelengths can be absorbed by photovoltaic layers and converted toelectrical energy, which is recycled within the electrical system, forexample to assist driving the backlight.

Alternatively, the narrow band filtering and the recycling of unusedwavelengths from the light source can be made to occur adjacent to thelight source, prior to propagation of light to a light guide. Referringnow to FIG. 9, an embodiment of the present disclosure includes a filmlayer including filtering and recycling elements positioned adjacent toa light source. The film layer can include a glass substrate 54, havingconversion materials 62 and 64 deposited on a first side of thesubstrate 54, and multi-bandpass filter 56 deposited on a second side.According to an embodiment, the substrate 54 is positioned immediatelyadjacent an output surface of light source 50. The film layer can beused in combination with a conventional uniformity film, which serves tomore evenly distribute illumination at the interface from light sourceto a light guide. The light source 50 can be a broad spectrum lightsource, or a narrow spectrum. If light source 50 is a narrow spectrumlight source and broad spectrum illumination is preferred, a layer ofparticle 52 can be included with conversion materials 62 and 64. Theconversion materials 62 and 64 and filter 56 operate in the mannerdescribed in the several embodiments herein to pass narrow bandemissions according to the passbands of filter 56, and to recycle otherwavelengths.

Alternatively in an embodiment the final LCD color filter elements canthemselves utilize a dichroic reflective filter. Rather than absorptionfilter elements for typical color filtering of the primary colorsub-pixel elements (e.g. red, green, blue), a novel color filter usingreflective dichroic filter will reflect light not of the desired primarycolor narrow wavebands, back through the LC element into the opticalstack. This can have the advantage of reducing the display thickness byintegrating dichroic coating layers.

In some OLED display embodiments, the pixels consist of point lightsources generated by OLED, with one emitting sub-pixel in each primarycolor (e.g. red, green, blue) and in some embodiments also includingwhite, forming a matrix of RGBW pixels. Alternatively, in other OLEDdisplay embodiments, the sub-pixels are broad-spectrum white pointsources, with a color filter placed over each white sub-pixel to createthe desired RGBW wavelength bandpass for each sub-pixel element. In someembodiments the first dichroic filter is located on top of the OLEDpixel forming a bandpass of a narrower emission bandwidth than theoriginal emitting elements. In other embodiments the final color filteris itself a dichroic filter, formed of independent narrow bandpassfilters for each primary color. Additionally a particle 52 located atthe OLED sub-pixel can assist in the recycling of light reflected,whereas an OLED display configured with white OLED sub-pixel elementsadditionally includes particles adapted to absorb light of unusedwavelengths and to re-emit in the desired sub-pixel primary wavelengths.

Dichroic filters have improved performance when light is incoming at aknown angle. The layers in the dichroic filter are constructed with anassumed angle of incident light and are most effective when light isentering at this angle, for example perpendicular to the surface of thefilter. Therefore, embodiments of the present disclosure include theaddition of a collimating structure near the light source, which can beused to enforce a particular angle of incidence on the dichroic filters.The collimating structure functions to funnel light, when placed on topof the light source and having reflective sides (e.g., ESR) that funnelincident light into a selected output angle. The illumination propagatedat the selected output angle collimates light onto the dichroic filters.A further benefit is the causing of light from the light source toilluminate a more constrained area of the display, which promotes thecapability of regional backlighting. In other embodiments the dichroicfilter is constructed with the assumption that light enters the filterat an acute angle of incidence, based on the construction of the lightsource and the reflective aspects of elements in the recycling assembly.In such embodiments the dichroic filter is designed such that the angleof reflection of the dichroic filters, and other reflective elements inthe assembly, is leveraged to steer the light in or near the optimalangle of incidence into the final dichroic filter (e.g., within +/−15degrees of the nominally optimal angle of incidence). In general,dichroic filter construction can be optimized to be effective over arange of angles of incidence.

In other embodiments the use of inverse prismatic elements in theoptical layers (for example including layers known as BacklightEnhancement Film “BEF”, Dual Brightness Enhancement Film “DBEF”, such asthe BEF, DBEF films supplied by 3M Corp.), are arranged between andbehind the backlight and display illumination surface, together withother reflective layers behind backlight light guide (such as ESRfilm-coating supplied by 3M corp), form a recycling assembly and areadapted to refract and reflect light not of preferred angles ofincidence to the display illumination surface. The purpose of BEF/DBEFand ESR is to reflect and recycle light not of a desired angle ofincidence to the output surface, and to intensify the output of lightfrom display panel, in a cone-like region that matches the typicalviewer position. In such embodiments, light rays are recycled within theprismatic-reflecting assembly until emitted in substantially the desiredangle of incidence, which is substantially normal to the displayillumination surface. In one embodiment the dichroic filter is placedafter the enhancement film to leverage the arrival of light entering thedichroic filter already at the optimal angle of the incidence, withrespect of the filter surface, as aligned with display output surface.

In one embodiment the layers of the dichroic filter are constructed soas to reflect and refract selected wavelengths along a selected angle ofincidence, at a normal to the dichroic filter plane. In otherembodiments the layers are constructed so as to reflect and refractdesigned wavelengths at an angle other than the normal of the dichroicfilter plane, but substantially along a pre-determined angle ofincidence. An example of this is where a dichroic filter layer is coatedon a surface of a light-guide assembly, which is designed to acceptlight at an angle to the transmission path, and direct it towards theselected path.

In other embodiments a dichroic filter is layered on top of thereflective element so as to refract light not of selected wavelengths,into a steeper angle of incidence within the Backlight Reflector (ESR) &Enhancement Layers (BEF/DBEF), enhancing the recycling of light not ofthe selected pass-band, between ESR, DBEF/BEF and light wavelengthconversion material. In other embodiments a dichroic filter and lightwavelength conversion material, are layered on top of the reflectiveelement so as to absorb, convert and re-emit light not of selectedwavelength, while reflecting light of the selected wavelength towardsthe angle of display emission.

While embodiments thus described have mainly been described in thecontext of a display having three primary colors, a greater (or lesser)number of primaries are possible and consistent with the invention.Referring now to FIG. 10, an embodiment of a multi-bandpass filterincludes narrow passbands for five primary wavelengths, centered at 467,495, 532, 573, and 630 nm (e.g., red, green, blue, cyan, and yellowprimaries). A benefit of an increased number of primaries is a widergamut of color representation for a display. A filter such as shown inFIG. 10 is consistent with the aforementioned embodiments.

The foregoing description, for purpose of explanation, has beendescribed with reference to specific embodiments. However, theillustrative discussions above are not intended to be exhaustive or tolimit the invention to the precise forms disclosed. Many modificationsand variations are possible and contemplated in view of the aboveteachings, including combinations of embodiments not explicitly recitedas such. The embodiments were chosen and described in order to explainthe principles of the invention and its practical applications, tothereby enable others skilled in the art to utilize the invention andvarious embodiments with various modifications as may be suited to theparticular use contemplated.

Embodiments according to the invention are thus described. While thepresent disclosure has been described in particular embodiments, itshould be appreciated that the invention should not be construed aslimited by such embodiments, but rather construed according to the belowclaims.

1-65. (canceled) 66: An assembly for adjusting the spectral emissions oftransmitted light of a liquid crystal display, comprising: a lightsource having an emission output surface operable to output light into abacklight assembly; a light guide adapted to receive incident light fromthe light source at a first surface, and to emit light at a secondsurface; a color filter surface containing a plurality of pixelcolor-filtering elements disposed between a plurality oflight-transmitting pixel elements of the liquid crystal layer and anillumination surface of a display; a collimating layer interposedbetween the light source and a first reflective filter and adapted tocollimate output light prior to incidence on the first reflectivefilter; and a first reflective filter interposed between the collimatingsurface and the illumination surface of the display, wherein the firstreflective filter is operable to pass at least one wave-band ofwavelengths of light source transmitted light, and to reflectwavelengths not of the multi-band, wherein a surface of photo-emissivecolor-conversion pixel elements is operable to absorb a wavelength oflight source light, and configured to emit in at least one waveband ofthe multi-band substantially transmitted by the pixel color filterelements. 67: The assembly of claim 66 wherein the first reflectivefilter is disposed adjacent to the light source output surface andbetween the light source and the light guide. 68: The assembly of claim66 wherein the first reflective filter is disposed within an opticalstack between the light guide and the color conversion surface of thedisplay. 69: The assembly of claim 66 further including a collimatingstructure interposed between the light source and the first reflectivefilter and adapted to collimate output light prior to incidence on thereflective filter. 70: The assembly of claim 66, additionally comprisinga second reflective filter disposed between the plurality of conversionpixel elements and the illumination surface, and operable to permittransmission of converted light of a multi-band, and to reflect lightnot of the multi-band. 71: The assembly of claim 66 wherein themulti-band of transmitted wavelengths corresponds with wavelengths ofpixel primary colors in the visible spectrum. 72: The assembly of claim70 wherein the color-conversion pixel elements comprise at least onelight recycling particle operable to absorb light reflected by areflective filter and to convert at least a portion of the excitationwavelength light into at least of a set comprising: the waveband of apixel color component, the excitation waveband of a light emitting colorconversion particle, the excitation waveband of a light recyclingparticle, and electrical energy. 73: The assembly of claim 66, whereinthe reflective filter comprises a dichroic filter. 74: A display system,comprising: a display module comprising an outer illumination surfaceand containing an array of light-emitting pixels comprising separateprimary-color waveband elements of a first multi-band; a plurality oflight sources operable to emit light towards the pixelated illuminationsurface of the display panel; a first reflective filter layer disposedadjacent the plurality of light sources and operable to reflect lightsource light over a second multi-band of wavelengths, and to transmitwavelengths not of the second multi-band; a color conversion layercomprising a composition of color converting particles disposed toreceive transmitted light source light and reflected light and operableto absorb in at least one of the received wavelength bands, and to emitat the at least one selected wavelength bands of the first multi-band; acolor filter surface containing a plurality of pixel color-filteringelements of distinct primary color wavebands disposed in a light pathbetween the color conversion layer and the illumination surface of thedisplay panel; and wherein the first reflective filter, the colorconversion layer, and the color filter elements form an arrangementdisposed between the light emission source and the illumination surfaceof the display panel. 75: The system of claim 74, wherein the colorconverting layer includes a recycling element comprising a firstparticle adapted to absorb light source wavelengths, and to emitrecycled light at a wavelength not of the multi-band wavelengths, and asecond particle adapted to absorb recycled light and to emit light at awavelength of the multi-band. 76: The system of claim 75, wherein therecycled light is of a shorter wavelength than the light sourcewavelengths. 77: The system of claim 75, wherein the recycled light isof a longer wavelength than the light source wavelengths. 78: The systemof claim 75 wherein the light source wavelengths are visible wavelengthsand the first particle is adapted to emit light at invisiblewavelengths, and wherein the second particle is adapted to absorb lightof less-visible wavelengths. 79: The system of claim 75, wherein thefirst particle and the second particle are disposed in adjacentdeposition layers, and wherein the first reflective filter issubstantially parallel to the adjacent deposition layers. 80: The systemof claim 74, further comprising a collimating layer interposed betweenthe light source array and the first reflective filter, and wherein thecollimating layer is adapted to collimate output light prior toincidence on the first reflective filter. 81: The system of claim 74,wherein a second reflective filter layer operable to receive the lightsource light and color conversion layer light, and to transmit at leastone selected wavelength of the first multi-band, and to reflect lightnot of the first multi-band. 82: The system of claim 74, wherein apolarizing layer comprising a plurality of polarizing elements disposedbetween the reflective filter and the color conversion elements, andoperable to transmit light of a selected polarization, and not transmita light not of the selected polarization. 83: The system of claim 74,wherein the multi-band comprises wavelengths in the visible spectrumaligned with the multi-band of the color filter primary-color wavebands.84: The system of claim 83, wherein the first reflective filter isoperable to reflect less-visible wavelengths. 85: The system of claim 74further comprising a layer containing light recycling particles disposedbetween the first and the second reflective filters, wherein the lightsource recycling layer is operable to convert reflected wavelengths intowavelengths substantially in the excitation range of the colorconversion particle layer. 86: The system of claim 74, wherein thecolor-filter surface comprises an array of reflective filter elements,wherein the reflective filters are configured to transmit light in thefirst multi-band, and reflect light not of the first multi-band. 87: AnOLED display assembly comprising: a plurality of OLED light emittingsources configured in an array of pixels emitting light towards theillumination surface of a display panel; a reflective layer disposedbehind the light emitting sources and configured to redirect lightsubstantially towards the illumination surface; a reflective filterdisposed in a light path of the light sources and operable to reflectlight of a first multi-band of wavelengths, and to transmit wavelengthsnot of the first multi-band; an array of pixel color conversion elementscomprising at least one particle disposed to receive light from thepixel emitter light sources, and operable to absorb light at a firstwavelength band and to emit light in at least one second wavelength bandof the first multi-band; and a polarizing element disposed to receiveemitted light of the color conversion element and transmit light of aselected polarization, and not transmit light not of the selectedpolarization. 88: The system of claim 87, wherein the reflective layeris in a bottom electrode of the OLED emitter and is further configuredto alter the polarization of reflected light. 89: The assembly of claim87 wherein the color conversion element comprises an additionalrecycling conversion particle adapted to absorb reflected light from thereflective filters, and to emit light at a third wavelength, and anadditional conversion particle adapted to absorb light of the thirdwavelength, and to emit light in at least one wavelength of the firstmulti-band of wavelengths. 90: The assembly of claim 87, furthercomprising a photovoltaic conversion element including a particleoperable to absorb light at a conversion wavelength band and to convertat least a portion of the conversion wavelength light into electricalenergy. 91: The assembly of claim 87 wherein the color filter integratesthe reflective filter.